Substantially native meniscal cartilage heterografts

ABSTRACT

The invention provides an article of manufacture comprising a substantially native xenogeneic knee meniscal cartilage heterografts for implantation into humans. The invention further provides a method for preparing a substantially native xenogeneic knee meniscal heterograft by removing at least a portion of a meniscus from a non-human animal to provide a heterograft; and washing the heterograft in saline and alcohol. In accordance with the invention the heterograft has substantially the same mechanical properties as the native xenogeneic meniscus.

This is a continuation of U.S. application Ser. No. 08/568,309 filed on Dec. 6, 1995, abandoned Nov. 22, 1996, and a continuation in part of U.S. application Ser. No. 08/483,256, filed on Jun. 7, 1995.

The present invention relates to the field of treatment of injured human knee joints, and in particular, to replacement and repair of a damaged human knee joint meniscus using a substantially native meniscus from a non-human animal.

BACKGROUND OF THE INVENTION

The human knee is a complex joint containing spatially interrelated bones, ligaments, and cartilaginous structures which interact to create a variety of motions. Specifically, the femoral condyles articulate with the surface plateaus of the tibia, through the cartilaginous medial and lateral menisci, and all of these structures are held in place by various ligaments. By virtue of their cartilaginous nature, the medial and lateral menisci are structures comprised of cells called fibrochondrocytes, an interstitial matrix of fibers of the protein collagen, and within a ground substance formed from proteoglycans. Undamaged menisci provide shock absorption for the knee by ensuring proper force distribution, stabilization, and lubrication for the interacting bone surfaces within the knee joint, which are routinely exposed to repeated compression loading during normal activity. Much of the shock absorbing function of the medial and lateral menisci is derived from the elastic properties inherent to cartilage. When menisci are damaged through injury, disease, or inflammation, arthritic changes occur in the knee joint, with consequent loss of function.

Since joint cartilage in adults does not naturally regenerate to a significant degree once it is destroyed, damaged adult menisci have historically been treated by a variety of surgical interventions including removal and replacement with prosthetic devices. An artificial knee joint having a rigid plastic femoral member and a metal tibial member is disclosed in U.S. Pat. No. 4,034,418. A number of meniscus prostheses have been devised which employ resilient materials such as silicone rubber or natural rubber, as in U.S. Pat. Nos. 4,344,193 and 4,502,161. Additional deformable, flexible resilient materials for a meniscus prosthesis such as collagen, tendon, or fibrocartilage are disclosed in U.S. Pat. Nos. 5,092,894 and 5,171,322. A cartilage replacement apparatus constructed of polyethylene plastic filled with small ball bearings or gelatinous fluid is described in U.S. Pat. No. 5,358,525. However, the known artificial prostheses have been unsatisfactory for treatment of damaged menisci, since they are deficient in the elastic, and therefore in the shock-absorbing, properties characteristic of natural menisci. Moreover, the known artificial devices have not proven able to withstand the forces inherent to routine knee joint function.

The present inventor provided improved prosthetic menisci in several of his earlier patents (U.S. Pat. Nos. 4,880,429; 5,007,934; 5,116,374; and 5,158,574). These patents generally disclose prosthetic menisci formulated from dry, porous matrices of processed natural fibers such as reconstituted cross-linked collagen, which optionally include glycosaminoglycan molecules. Generally, the source of collagen for these prosthetic menisci has been animal Achilles tendons or skin. The reconstitution process removes non-collagenous materials such as glycoproteins, proteoglycans, lipids, native glycosaminoglycans, and the like, which may confer additional elastic properties to the original tissue.

Much of the structure and many of the properties of original tissues may be retained in transplants through use of xenogeneic or heterograft materials, that is, tissue from a different species than the graft recipient. For example, tendons or ligaments from cows or other animals are covered with a synthetic mesh and transplanted into a heterologous host in U.S. Pat. No. 4,400,833. Flat tissues such as pig pericardia are also disclosed as being suitable for heterologous transplantation in U.S. Pat. No. 4,400,833. Bovine peritoneum fabricated into a biomaterial suitable for prosthetic heart valves, vascular grafts, burn and other wound dressings is disclosed in U.S. Pat. No. 4,755,593. Bovine, ovine, or porcine blood vessel heterografts are disclosed in WO 84/03036. However, none of these disclosures describe the use of a xenograft for meniscus replacement.

Xenograft materials must be chemically treated to reduce immunogenicity prior to implantation into a recipient. For example, glutaraldehyde is used to cross-link or "tan" xenograft tissue in order to reduce its antigenicity, as described in detail in U.S. Pat. No. 4,755,593. Other agents such as aliphatic and aromatic diamine compounds may provide additional crosslinking through the sidechain carboxyl groups of aspartic and glutamic acid residues of the collagen polypeptide. Glutaraldehyde and diamine tanning also increases the stability of the xenograft tissue.

Xenograft tissues may also be subjected to various physical treatments in preparation for implantation. For example, U.S. Pat. No. 4,755,593 discloses subjecting xenograft tissue to mechanical strain by stretching to produce a thinner and stiffer biomaterial for grafting. Tissue for allograft transplantation is commonly cryopreserved to optimize cell viability during storage, as disclosed, for example, in U.S. Pat. Nos. 5,071,741; 5,131,850; 5,160,313; and 5,171,660. U.S. Pat. No. 5,071,741 discloses that freezing tissues causes mechanical injuries to cells therein because of extracellular or intracellular ice crystal formation and osmotic dehydration.

SUMMARY OF THE INVENTION

The present inventor has surprisingly discovered that a substantially non-immunogenic meniscal cartilage heterograft for implantation into a human in need of knee meniscus repair may be produced by the steps of removing at least a portion of a medial or lateral meniscus from a knee joint of a non-human animal to provide a heterograft; and washing the heterograft in water and alcohol. The heterograft of the invention, since it requires no further processing steps, is believed to represent a meniscal cartilage in its in vivo form and is thus termed a "substantially native" meniscal cartilage heterograft. The heterograft of the invention retains its in vivo mechanical properties such as elasticity and load-bearing capabilities. The invention further provides a method for making the substantially native meniscal cartilage heterograft.

In one embodiment, the invention provides an article of manufacture comprising a substantially native knee meniscal cartilage heterograft for implantation into a human, produced by removing at least a portion of a medial or lateral meniscus from a knee joint of a non-human animal to provide a heterograft; and washing the heterograft in water and alcohol, whereby the heterograft has substantially the same mechanical properties as an in vivo meniscus.

In another embodiment, the invention provides a method of preparing a substantially native knee meniscal heterograft for implantation into a human, which comprises removing at least a portion of a medial or lateral meniscus from a knee joint of a non-human animal to provide a heterograft; and washing the heterograft in water and alcohol, whereby the heterograft has substantially the same mechanical properties as the meniscus.

BRIEF DESCRIPTION OF THE DRAWINGS

The various features of the invention may be more fully understood from the following description when read together with the accompanying drawings.

FIG. 1 shows a simplified diagrammatic representation of a human knee joint 3, with medial meniscus 7 and lateral meniscus in their native positions.

FIG. 2 is a diagrammatic representation of a cut-away view of a human knee joint 3, showing the medial meniscus 7 and lateral meniscus 8 as they are positioned in vivo over the medial and lateral condyles of the tibia.

FIG. 3 is a diagrammatic representation of resection of a torn lateral meniscus of a human knee, and preparation of the knee for receipt of a meniscal implant.

FIG. 4 is a diagrammatic representation the preferred drill guide placement for posterior lateral meniscal horn insertion into a human knee.

FIG. 5 is a diagrammatic representation of a cannulated drill overdrilling guide wire at the posterior lateral meniscal horn insertion into a human knee.

FIG. 6 is a diagrammatic representation of the appearance of a human knee with posterior and anterior drill holes for meniscal horn insertion.

FIG. 7 is a diagrammatic representation of the preferred suture passer placement for pulling a meniscal implant into a human knee joint.

FIG. 8 is a diagrammatic representation of the appearance of a human knee containing a meniscal implant during the insertion stage.

FIG. 9 is a diagrammatic representation of the appearance of a human knee containing a meniscal implant with zone-specific meniscal repair sutures in place for final tying of the meniscal repair sutures.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

The substantially native xenogeneic meniscal cartilage heterograft produced in accordance with the method of the invention generally maintains the mechanical properties of a functional in vivo meniscus. The substantially native meniscal cartilage heterograft produced by the method of the invention produces little or no immunological response in the human into which it is implanted, and is therefore substantially non-immunogenic. While the meniscus may undergo a slight amount of shrinkage during processing, a substantially native xenogeneic medial meniscus heterograft prepared in accordance with the invention will have the general appearance of a native medial meniscus, and a substantially native xenogeneic lateral meniscus heterograft of the invention will have the general appearance of a native lateral meniscus. The substantially native xenogeneic meniscal heterograft of the invention may also be cut into segments, each of which may be implanted into the knee of a recipient as set forth below.

The invention provides, in one embodiment, a method for preparing or processing a substantially native xenogeneic medial or lateral meniscus for engraftment into humans. As defined herein, "xenogeneic" means any non-human animal. Thus knee menisci may be harvested from any non-human animal to prepare the heterografts of the invention. Menisci from transgenic non-human animals or from genetically altered non-human animals may also be used as heterografts in accordance with the present invention. Preferably, bovine, ovine, or porcine knee joints serve as sources of the medial and lateral menisci used to prepare the heterografts. More preferably, immature pig, calf or lamb knee joints are the sources of the menisci, since the cartilage of younger animals may be inherently more elastic and engraftable than that of older animals. Most preferably, the age of the source animal is between six and eighteen months at time of slaughter.

In the first step of the method of the invention, an intact medial or lateral meniscus is removed from the knee of a non-human animal. The joint which serves as the source of the menisci should be collected from freshly killed animals and preferably immediately placed in a suitable sterile isotonic or other tissue preserving solution. Harvesting of the joints should occur as soon as possible after slaughter of the animal and should be performed in the cold, i.e., in the approximate range 5-20° C., to minimize enzymatic and/or bacterial degradation of the meniscal tissue. The menisci are harvested from the joints in the cold, under strict sterile technique. The joint is opened by first transecting the patellar tendon. The horns of the menisci are dissected free of adhering tissue. A small amount of bone representing a substantially cylindrical plug of approximately five millimeters in diameter by five millimeters in depth may be left attached to the horns. The meniscal synovial junction is carefully identified and freed from the meniscus tissue itself, thereby forming the heterograft.

The heterograft is then washed in about ten volumes of sterile cold water to remove residual blood proteins and water soluble materials. The heterograft is then immersed in alcohol at room temperature for about five minutes, to sterilize the tissue and to remove non-collagenous materials. A heterograft appears as a shiny "C"-shaped fibrous tissue, having generally a crescent-shaped principal surface on the top side (the "superior surface") and a generally crescent-shaped principal surface on the bottom side (the "inferior surface"), where the outer portions of the superior and inferior surfaces are joined by way of an outer lateral surface and the inner portions of the superior and inferior surfaces are joined by way of an inner lateral surface.

Prior to use, the outer lateral surface of the heterograft may optionally be pierced to increase permeability to fibrochondrocytes after implantation. A sterile surgical needle such as an 18 gauge needle may be used to perform this piercing step, or, alternatively a comb-like apparatus containing a plurality of needles may be used. The piercing may be performed with various patterns, and with various pierce-to-pierce spacings, in order to establish a desired access to the interior of the heterograft. Piercing may also be performed with a laser. In one form of the invention, one or more straight lines of punctures about three millimeters apart are established circumferentially in the outer lateral surface of the heterograft.

Prior to implantation, the substantially native meniscal cartilage heterograft of the invention may be treated with limited digestion by proteolytic enzymes such as ficin or trypsin to increase tissue flexibility, or with glycosidases to remove surface carbohydrate moieties, or coated with anticalcification agents, antithrombotic coatings, antibiotics, growth factors, or other drugs which may enhance the incorporation of the heterograft into the recipient knee joint. The substantially native meniscal cartilage heterograft of the invention may be further sterilized using known methods, for example, with glutaraldehyde or formaldehyde treatment, ethylene oxide sterilization, propylene oxide sterilization, or the like. The substantially native meniscal cartilage heterograft may be stored frozen until required for use.

The substantially native meniscal cartilage meniscal heterograft of the invention, or a segment thereof, may be implanted into damaged human knee joints by those of skill in the art using known arthroscopic surgical techniques. Specific instruments for performing arthroscopic techniques are known to those of skill in the art, which ensure accurate and reproducible placement of meniscal implants. For meniscal cartilage replacement to succeed, the following goals are preferably accomplished:

1. The torn fragmented pieces of native meniscal cartilage must be removed.

2. The attachment sites for the meniscal horns must be anatomically placed.

3. The periphery of the meniscal implant must be attached securely enough to permit axial and rotational loads.

4. The surrounding capsule and ligaments of the knee joint must be neither excessively violated nor constrained by the fixation technique. The method of meniscal implantation described in detail below is derived from K. R. Stone, et al., Arthroscopy: The Journal of Arthroscopic and Related Surgery 9, 234-237 (1993); other methods of meniscal implantation may also be employed to use the xenogeneic meniscal heterografts of the present invention.

Initially, complete diagnostic arthroscopy of the knee joint is accomplished using known methods. If anterior cruciate ligament surgery is to be performed simultaneously, the femoral and tibial tunnels for the cruciate reconstruction should be drilled first. The torn portion of the meniscal cartilage is evaluated. If meniscal repair cannot be accomplished due to severity of the tear or poor quality of the tissue, then preparation of the meniscal rim is undertaken by removing the torn portions of the cartilaginous tissue (FIG. 3). When the entire human meniscus is to be replaced by a xenogeneic meniscus heterograft of the invention, nearly all of the human meniscus is removed. Additionally, for replacement of the entire human meniscus with a substantially native xenogeneic meniscal cartilage heterograft of the invention, resection of the human meniscal horns and preparation of bony tunnels to accept bone plugs may be required. When only a portion of the human meniscus is to be replaced with a segment of the substantially native xenogeneic meniscal cartilage heterograft of the invention, only the damaged portions are removed, preserving the peripheral rim and horns for attachment of the xenogeneic meniscus heterograft segment. If absolutely no human meniscal rim is present, then partial replacement of the meniscus should not be performed. If the joint is excessively tight, a joint distractor may be applied or the medial collateral ligament may be partially released.

For medial or lateral meniscal replacement, the arthroscope is placed in the mid-lateral or anterior lateral portal and the tibial guide is placed through the anterior medial portal. The tip of the guide is brought first to the posterior horn of the meniscus. It should be noted that the posteromedial horn inserts on the posterior slope of the tibial eminence. A drill pin is then brought from the anterior medial side of the tibial tuberosity to the posterior horn insertion (FIG. 4). The pin placement can be confirmed by passing the arthroscope through the intercondylar notch and viewing the exit site of the pin. Extreme care must be undertaken to avoid penetration through the posterior capsule of the knee, endangering the neurovascular bundle. When the pin position is confirmed, the pin is then overdrilled with a 4.5-mm cannulated drill bit with the option of a drill stop to prevent posterior capsular penetration (FIG. 5). The bit is left in place and used as a tunnel for passage of a suture passer with a suture such as a #2 ETHIBOND™ suture available from Johnson & Johnson. The suture is passed up the bore of the drill bit, the drill bit removed, and the suture left in place.

The anterior medial meniscus insertion point in humans varies considerably, most often being found anterior to the medial tibial eminence. The anterior horn of the lateral meniscus inserts just posterior to the anterior cruciate ligament. An anterior drill hole is made by first identifying the insertion point of the anterior horn of the lateral meniscus, by placing the tip of the drill guide so that a relatively vertical hole will be made (FIG. 6). The drill pin is placed, then the cannulated drill bit is used to overdrill the drill pin placement to form the anterior drill hole. A suture passer is placed in the anterior drill hole. Alternatively, the anterior horn of the medial meniscus is affixed with a suture anchor directly to bone as opposed to a drill hole.

Before the suture is grasped from the anterior and posterior drill holes, the anterior portal is widened to approximately 2 cm. The suture grasper is then passed through the widened portal, and both the anterior and the posterior sutures brought out simultaneously. This technique prevents the sutures from becoming entangled in two different planes of the fat pad and capsular tissue.

The heterograft is now brought onto the field. Two horizontal mattress sutures, for example, #2-0 Ethibond™ sutures or the like, are placed through each horn of the xenogeneic meniscus heterograft with the free ends exiting the inferior surface (FIG. 7). The two posterior sutures are then drawn through the knee and out the posterior tibial tunnel (FIG. 8). If viewing from a mid-lateral portal, the anterolateral portal can be used for probe insertion to push the implant medially into place through a 1-inch incision. No insertion cannula is required. The anterior sutures are then similarly passed. The horn sutures are then tied over the anterior tibial bony bridge.

Next, zone specific meniscal repair cannulae are brought into place. For medial insertions, a posterior medial vertical incision is made one third of the distance from the back of the knee for protection of the saphenous nerve and for retrieval of the inside-out meniscal repair needles. A second vertical incision is usually required further anteriorly, next to the anterior medial arthroscopy portal, to capture the anterior exiting needles. Through these two incisions, the suture needles can be captured and the knots placed directly over the capsule (FIG. 9).

When using the meniscal repair needles, the posterior cannulae should be used first, with the sutures placed vertically and evenly spaced. The repair should proceed from posterior to anterior so that a buckle is not produced within the heterograft. Each knot is tied as it is placed to avoid the chance of suture tangling. The knots are spaced approximately 4 mm apart. The knee is cycled through several complete ranges of motion of ensure that the heterograft moves smoothly without impingement.

When performing a lateral meniscal replacement, the medial portal is suitable for heterograft insertion. This may require excision of the ligamentous mucosa and removal of a portion of the fat pad. The drill guide for the posterior horn of the lateral meniscus is inserted through the anteromedial portal. The posterior slope of the lateral tibial spine must be identified for accurate meniscal horn insertion. The anterior horn inserts on the anterior slope of the lateral tibial spine in approximation to the lateral aspect of the anterior cruciate ligament. The advantage of drilling these holes from the medial side is that the tunnel divergence will be greater, providing a larger bony bridge between the horn insertions. The remainder of the insertion technique remains the same, except that great care should be taken to protect the neurovascular bundle when suturing the posterior horn. Accessing posterolateral exposure is necessary to safeguard the common peroneal nerve and to expose the lateral capsule. If there is any doubt about the suture placement, open posterior horn suturing should be performed in the standard fashion.

Routine skin closure and dressings are applied. Thirty milliliters of 0.5% Marcaine (Astra) with epinephrine may be instilled if desired. A postoperative hinged knee brace is applied with the range of motion limited to 30° of extension and 90° of flexion.

Postoperatively the patient is permitted touchdown weight bearing in a hinged knee brace for six weeks. The brace is removed for sleeping and out-of-brace range-of-motion exercises. On day one after surgery, exercises are initiated for quad strengthening, including leg raises, quad sets, and well-leg bicycling. After six weeks, knee-bend exercises, two-leg bicycling, and water running exercises are initiated. When maximal strength gains are achieved, pivoting sports can be resumed, usually at four to six months after surgery.

Those of skill in the art will recognize that the invention may be embodied in other specific forms without departing from the spirit or essential characteristics thereof. The presently described embodiments are therefore to be considered in all respects as illustrative and not restrictive, the scope of the invention being indicated by the appended claims rather than by the foregoing description, and all variations of the invention which are encompassed within the meaning and range of equivalency of the claims are therefor intended to be embraced therein. 

What is claimed is:
 1. A method of preparing a meniscal cartilage heterograft for implantation into a human, which comprisesa. removing at least an intact portion of a native meniscal cartilage from a joint of a non-human animal to provide a heterograft; b. washing the heterograft in water and alcohol; and c. digesting the heterograft with at least one glycosidase to remove surface carbohydrate moieties from the heterograft;whereby the heterograft has substantially the same mechanical properties as the native meniscal cartilage.
 2. The method according to claim 1, wherein the step of removing the portion of said cartilage further comprises removing the portion to establish a heterograft having a superior principal surface and an inferior principal surface, each of said superior principal and inferior principal surfaces having an outer portion joined by an outer lateral surface, and each of said superior principal and inferior principal surfaces having an inner portion joined by an inner lateral surface.
 3. The method according to claim 1, comprising the step performed prior to step c of piercing the removed portion of said cartilage at one or more points.
 4. The method of claim 1, comprising the step following step c of treating the heterograft with one or more agents selected from the group consisting of anticalcification agents, antithrombotic agents, antibiotics, and growth factors.
 5. The method of claim 1, comprising the step following step c of sterilizing the heterograft.
 6. The method of claim 5, wherein said step of sterilizing the heterograft is selected from the group consisting of treatment with glutaraldehyde, treatment with formaldehyde, treatment with ethylene oxide, and treatment with propylene oxide.
 7. The method of claim 1 comprising the step ofprior to step c, treating the heterograft with a second enzyme.
 8. The method of claim 7 wherein said second enzyme is selected from the group consisting of ficin and trypsin. 